In a conventional conference telephone or "speakerphone," a desktop or base unit is provided which has a loudspeaker and a microphone, both of which are utilized during a conference call. Audio amplifiers are also provided to amplify the signals received from a telephone central office (that is, signals from a "far" party) to a level that is sufficient to drive the loudspeaker, and to amplify signals coupled by the microphone prior to transmission to the telephone central office (that is, signals from a "near" party). A handset having its own speaker and microphone are provided for private telephone conversations.
Because the microphone and loudspeaker in a conventional speakerphone are both mounted within the same physical enclosure and are generally proximate one another, there is a degree of acoustic coupling between the far party speech reproduced by the loudspeaker and the near party speech received at the microphone. Such coupling typically is suppressed, using an echo suppression circuit, or canceled using an echo canceling circuit. However, when the magnitude of the far party speech is great, it is difficult for the echo canceling circuit to rapidly, accurately and smoothly determine whether the audio signals constitute "near" or "far" party signals. This is particularly true during moments when both parties are speaking insofar as the far party speech may dominate the near party speech level at the microphone. As a result, even with the use of echo canceling circuitry, there can be noticeable switching or cutting out of the speech from one or both of the parties and/or a palpable reduction in the gain of the signal in an effort to reduce undesired acoustic coupling.
These problems have been recognized in the art and various approaches have been proposed. For one approach directed to continual adjustments of an echo canceling tap profile to maintain loop stability, see application Ser. No. 09/090,733, filed: Jun. 4, 1998, for SPEAKERPHONE CONTROL BASED ON ECHO CANCELER TAP PROFILE, assigned to the present assignee and hereby incorporated in its entirety by reference. The '733 patent application also provides a thorough description of the operation and circuitry of a conference telephone.
However, what still is needed in the art is an improved conference telephone which addresses these problems and improves the efficacy of conventional canceling circuits by permitting the loudspeaker and microphone to be universally positioned relative to one another.